title: Unusual magnetism in templated NiS nanoparticles.
abstract: Nanostructured NiS was prepared by inclusion into anodic alumina templates. The resultant particles were found to be stoichiometric and highly crystalline. The particles displayed small particle superparamagnetism, and a low temperature (at 48 K (T(sg))) spin-freezing phenomenon (a spin-glass) and higher temperature (170 K) thermal blocking of small particle magnetic moment fluctuations were both observed for the first time for a sulfide material. Very unusually, these NiS materials are quite distinct from antiferromagnetic nanoparticulate sulfide materials, as they display a high temperature ferromagnetic-like phase. The saturation magnetization, the remanent magnetization, the coercivity and the ferromagnetic mass susceptibility were measured as 0.58 emu g( - 1) (at 100 K), 0.19 emu g( - 1), 219.5 Oe (at 170 K) and ∼ 900 × 10( - 6) emu Oe( - 1) g( - 1) respectively and these are consistent with a moderately strong ferromagnetism. The materials had an unexpectedly high Curie temperature of 390 K. The decrease of the saturation magnetization value at 30 K suggests that the ferromagnetic response is a surface phenomenon and the high coercivity of the paramagnetic component well above T(sg) suggests that the core can be described as superparamagnetic.
authors.affiliation: Department of Chemistry, University College Cork, Cork, Republic of Ireland.
authors.forename: Louise
authors.initials: L
authors.lastname: Barry
authors.forename: Justin D
authors.initials: JD
authors.lastname: Holmes
authors.forename: David J
authors.initials: DJ
authors.lastname: Otway
authors.forename: Mark P
authors.initials: MP
authors.lastname: Copley
authors.forename: Olga
authors.initials: O
authors.lastname: Kazakova
authors.forename: Michael A
authors.initials: MA
authors.lastname: Morris
mesh_terms: D008280:Magnetics; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology; D009532:Nickel / Q000737:chemistry*
chemical_list: D009532:Nickel; C017558:nickel sulfide